I would have to agree with Mr.Henry. I suggest you use the the puddle in the middle of the concrete patio to make money to buy those expensive cannons. You should put some water in it and some tuna/catnip to attract neighborhood cats. Then you should attach some live electric wires to the puddle and sell the meat to a butcher for money. In no time you should have enough for the cannons to fix your concrete patio problem. Good luck on your project its a dusy!:)

There are several different brands of concrete that can be used to repair concrete and you can take to a feather edge. A good concrete supplier will have them. They are about $20 for a 45 lb bag and depending on the size of your patio it may take ten to 20 bags to fix the problem. Since this is a wearing surface you may have to take it to a quarter inch edge instead of a feather edge. You mix it up in a clean plastic trash can and then dump it on the patio and level it. If the job is big you may have to take it on in two or three different increments or get help to mix it up as you level it.